This project is designed to investigate the size and spatial distribution of cortical neuron "colonies" in the primate motor cortex that project to the spinal cord and are associated with individual muscles or closely related groups of muscles, as well as the activiy of neurons in such colonies during defined voluntary motor behaviors. Intracortical microstimulation (ICMS) is used to map regions that produce excitation or inhibition of particular muscles or muscle groups, and the resultant cortical maps are compared with those for snyergist or antagonist muscle groups. Cortical cell discharge patterns during normal movements are evaluated with respect to the excitation or inhibition of muscle activity that is produced by ICMS. Spinal cord organization of motoneurons innervating the two heads of flexor carpi ulnaris (FCU) was explored with nerve injections of HRP. No difference was found in the size or localization of the motoneuron innervating the two heads of FCU even though the heads are composed of pedominately different fiber types.